How American Football Works

Let's take a look at some of the standard features of a professional football field:

Sideline - The sideline is the 6-foot-wide (1.8-meter-wide) boundary line that runs the length of each side of the football field.

End line - The end line is a 6-foot-wide boundary line that connects the two parallel sidelines. The end line and sideline compose the rectangular shape of the field. Two pylons flank the end of the end line.

End zone - The end zones are two 10-yard-wide (9-meter-wide) areas at each end of the field inside the end line. The end zone behind a team is that team's end zone, and the end zone ahead of a team is its opponent's end zone.

Goal line - The goal line is an 8-inch-wide (20-cm-wide) line that runs across the front of the end zone. Two pylons flank the end of the goal line.

Yard lines and hash marks - In the 100 yards (91 meters) between goal lines, hash marks on either side of the field mark each yard. At every fifth yard, a solid white line runs from sideline to sideline, and at every 10 yards those lines are numbered (i.e., 10, 20, 30, 40, etc.). This crosshatch of lines gives the field its "gridiron" nickname.

Goalposts - Centered at the back of the end zone is a pole that extends 10 feet (3 meters) high and connects with a horizontal cross bar. On each end of the 18-foot, 6-inch (5.5-meter) cross bar is an upright post that rises to a height of 30 feet (9 meters) above the ground. A 4-inch by 42-inch (10-cm x 107-cm) ribbon is tied to the top of each upright.

­The most essential piece of equipment in a football game is the ball. Official NFL footballs are handmade by Wilson Sporting Goods Co. The football is an oblong sphere and is 11 to 11.5 inches (27.9 - 29.2 cm) long. It has a lengthwise circumference of about 28.5 inches (72.4 cm) and a width-wise circumference of about 21.5 inches (54.6 cm) in the middle of the ball. It weighs between 14 and 15 ounces (397 - 425 grams). The ball consists of an inflated, polyurethane bladder placed in cowhide covering and laced with gridcord material. Gridcord is cotton thread covered with vinyl. A three-ply, synthetic lining is sewn inside the leather covering to protect the bladder and help the football keep its distinct, elongated shape. A valve connected to the bladder protrudes through the leather and allows air to be pumped into the ball.

With the equipment identified and the field set, we can now play a game. An NFL game is divided into four quarters with an extended halftime break between quarters two and three. Each quarter is 15 minutes long. If the teams are tied after four quarters of play, they play an additional overtime period of 15 minutes. In the overtime, the first team to score wins.

While the game time adds up to one hour, it usually takes three to four hours to play a game. Teams can stop the clock by running out of bounds, throwing an incomplete pass, or calling a time-out, of which they have three per half. Time also stops for each of the two-minute warnings, observed two minutes prior to the end of the second and fourth quarters.